This invention relates to a single chip, low cost camera element for High Definition Television (HDTV). More specifically the invention relates to the use of acoustic charge transport in a gallium arsenide (GaAs) substrate to achieve high speed read out of photogenerated electric charge.
Existing HDTV cameras utilize a vacuum tube as the detecting element. One example of such a tube is the HARPICON H4318 manufactured by Hitachi. Although the HARPICON H4318 camera tube provides low noise, high sensitivity performance for HDTV applications, a camera using this tube is relatively large, fragile and heavy. Therefore, it is not well suited for use in light-weight applications such as hand-held HDTV broadcast cameras, camcorders, or space applications. For these applications a compact, light-weight, completely solid state device is ideal.
The conventional choice for a solid-state camera chip is one which uses a charge coupled device (CCD) to read out the image charge. However, there is presently only one CCD camera for HDTV which can operate at the required video frame rate. This camera, manufactured by Toshiba, is very costly and therefore unsuitable for consumer applications.
The HARPICON H4318 achieves high sensitivity and resolution by avalanche multiplication induced gain within the detection stage, which is made from amorphous selenium (a-Se). However, the use of an a-Se detector stage means that hole transport and collection are required because the hole ionization rate is substantially higher than the electron ionization rate in a-Se. Hole transport is not compatible with high speed integrated circuit operation.
Therefore, there is a need for a small, low-cost, low voltage, easy to manufacture, reliable, high resolution HDTV camera element, capable of read out speeds compatible with HDTV frame rate requirements.